Helium is generally produced by separation from a natural gas stream. An often used method for carrying out the separation is cryogenic processing.
Typically carbon dioxide is also present in the natural gas along with the helium. If cryogenic processing is to be employed to separate the helium from the natural gas to produce crude helium, it has heretofore generally been necessary to remove the carbon dioxide from the natural gas prior to the cryogenic processing. This is because at the low temperatures which cryogenic processing operates to produce crude helium, the carbon dioxide will freeze and plug or otherwise foul the processing equipment. Examples of carbon dioxide removal upstream of such cryogenic processing include contacting the feed with a liquid such as certain amines and/or passing the feed through molecular sieve beds for adsorption of the carbon dioxide. Such pretreatment systems increase both the capital and operating costs of a crude helium production system.
Accordingly it is an object of this invention to provide a cryogenic helium production system which can process a feed stream containing helium, hydrocarbon and carbon dioxide without need for a separate carbon dioxide removal step upstream of the cryogenic processing.
As mentioned, the helium is found with natural gas and the hydrocarbon is preferably recovered in addition to the helium. Typically the hydrocarbon is recovered at a relatively low pressure from the cryogenic separation and then compressed to higher levels for pipeline transmission. The relatively low pressure is the result of the cryogenic processing which operates more efficiently at lower pressures. However, it would be desirable to have a cryogenic processing system for producing crude helium which can also produce at least some hydrocarbon at higher pressure thus reducing compression requirements and therefore reducing costs.